There are various types of recording media, for example, magnetic disks, optical disks and magneto-optical disks, that record digital data such as music contents and video data therein. Since a semiconductor memory card as a sort of the recording media uses a semiconductor memory such as a flash ROM as a recording device to miniaturize the recording media, the semiconductor memory card has been rapidly spreading especially in compact portable equipment such as a digital still camera and cellular phone terminal.
Data stored in the semiconductor memory card is managed according to a file system and the user can easily handle the stored data as a file. Conventionally used file systems include a FAT file system disclosed in ISO/IEC9293, “Information Technology-Volume and file structure of disk cartridges for information”, 1994. In addition, there are UDF (Universal Disk Format) described in OSTA Universal Disk Format Specification Revision 1.50, 1997 and NTFS (New Technology File System). Since the semiconductor memory card in which the data is managed according to the file systems can share the file between equipments interpreting the same file system, data can be exchanged between the equipments.
The file system manages an information recording area for recording data by dividing the recording area into sectors as minimum access units and clusters as sets of sectors, and manages one or more clusters as a file. A free area is allocated in units of clusters as the area in which the data contained in the file is stored and the data contained in the file is not necessarily stored in a consecutive area. When a file which is not stored in the consecutive area is read or written, there has been a problem that the reading/writing rate becomes lower as compared with the case where a file stored in a consecutive area is read or written since a seek operation occurs during the reading or writing.
Conventionally, when a host device, for example, a video recording camera performs a data writing process for a semiconductor recording medium in real time, there has been a case where data rewriting process can not follow data loading process depending on usage state of the semiconductor recording medium, that is, the state of an internal data recording area. As a result, data rewriting cannot has become impossible, there has often been problems such as an interruption in video streaming.
Conventionally, a method for controlling data writing so as to store data for 1 page of a manuscript in the consecutive area in an image processing device is provided in Japanese Unexamined Patent Publication No. 2002-29101 as a method for solving the above-mentioned problems. In the conventional method, by necessarily writing data in a consecutive area having a fixed length in data writing, it can be secured that process can be certainly finished within a certain process time in data reading.
In Japanese Unexamined Patent Publication Sho63-228281 a memory card from which a host device can acquire a type, capacity and rate of a memory is disclosed. In unexamined Patent Publication Hei 1-76316 and Japanese Unexamined Patent Publication Hei 7-320018, a memory card which holds a plurality of transfer rates therein and switches the transfer rate in response to an instruction from a host is disclosed.
The above mentioned conventional arts, however, have the following problem. In the conventional control method, data size for 1 page of the draft as process unit of the image processing device is used as a unit of consecutive area. That is, the unit of consecutive area is determined based on the size suitable for data to be handled by an application. This method is effective for the recording medium which causes no difference in writing rate due to distinction of writing unit to the recording medium. However, in the semiconductor memory card, since the writing unit has a great influence on the writing rate and the relationship between the writing unit and writing rate varies depending on characteristics and management method of the semiconductor memory for use, an optimum access method for all semiconductor memory cards are not uniquely determined, and even when the data size is fixed as in the conventional example, it is impossible for all of the semiconductor memory cards to be accessed at high-rate.